The invention relates to knee prostheses which have a hinge for determining the flexion movement. This can be a hinge which is used exclusively for stabilization (DE-C-31 19 841, EP-A-716 839, EP-A-791 343, EP-A-420 460) or which transmits the full load (GB-C-1 305 391, EP-A-278184, FR-C-2 161 588, U.S. Pat. No. 3,772,709). The hinge is in each case formed by a hinge fork which is normally connected to the femur, and by a hinge centre piece which is connected to the tibia. The branches of the hinge fork and the centre piece have aligned bores through which a hinge pin passes. Generally, the femoral and tibial components of the prosthesis are first implanted separately and then connected to one another. In those cases where only the hinge pin connects the components to one another, it is pushed into the associated receiving bores from the side after the components have been implanted. This makes necessary a corresponding insertion opening in one of the femoral condyles, which adversely weakens the bone and involves additional work during the operation. In those prostheses which contain the hinge in a stabilizing part which is connected to the tibial component via a rotation bearing having a journal parallel to the tibia, the components are most often joined together by means of the journal which belongs to one component being inserted into the receiving bore of the other component. This has the disadvantage that the ligament apparatus of the knee has to be stretched considerably.